Development and application of novel BiFC probes for cell sorting based on epigenetic modification

The epigenetic signature of cancer cells varies with disease progression and drug treatment, necessitating the study of these modifications with single cell resolution over time. The rapid detection and sorting of cells based on their underlying epigenetic modifications by flow cytometry can enable single cell measurement and tracking to understand tumor heterogeneity and progression warranting the development of a live-cell compatible epigenome probes. In this work, we developed epigenetic probes based on bimolecular fluorescence complementation (BiFC) and demonstrated their capabilities in quantifying and sorting cells based on their epigenetic modification contents. The sorted cells are viable and exhibit distinctive responses to chemo-therapy drugs. Notably, subpopulations of MCF7 cells with higher H3K9me3 levels are more likely to develop resistance to Doxorubicin. Subpopulations with higher 5mC levels, on the other hand, tend to be more responsive. Overall, we report for the first time, the application of novel split probes in flow cytometry application and elucidated the potential role of 5mC and H3K9me3 in determining drug responses.

Identifying distinct heterochromatin regions using combinatorial epigenetic probes in live cells

The 3D spatial organization of the genome controls gene expression and cell functionality. Heterochromatin (HC), which is the densely compacted and largely silenced part of the chromatin, is the driver for the formation and maintenance of nuclear organization in the mammalian nucleus. It is functionally divided into highly compact constitutive heterochromatin (cHC) and transcriptionally poised facultative heterochromatin (fHC). Long regarded as a static structure, the highly dynamic nature of the heterochromatin is being slowly understood and studied. These changes in HC occur on various temporal scales during the cell cycle and differentiation processes. Most methods that capture information about the heterochromatin are static techniques that cannot provide a readout of how the HC organization evolves with time. The delineation of specific areas such as fHC are also rendered difficult due to its diffusive nature and lack of specific features. Another degree of complexity in characterizing changes in heterochromatin occurs due to the heterogeneity in the HC organization of individual cells, necessitating single cell studies. Overall, there is a need for live cell compatible tools that can stably track the heterochromatin as it undergoes re-organization. In this work, we present an approach to track cHC and fHC based on the epigenetic hallmarks associated with them. Unlike conventional immunostaining approaches, we use small recombinant protein probes that allow us to dynamically monitor the HC by binding to modifications specific to the cHC and fHC, such as H3K9me3, DNA methylation and H3K27me3. We demonstrate the use of the probes to follow the changes in HC induced by drug perturbations at the single cell level. We also use the probe sets combinatorically to simultaneously track chromatin regions enriched in two selected epigenetic modifications using a FRET based approach that enabled us tracking distinctive chromatin features in situ.

Monitoring Histone Methylation (H3K9me3) Changes in Live Cells

H3K9me3 (methylation of lysine 9 of histone H3) is an epigenetic modification that acts as a repressor mark. Several diseases, including cancers and neurological disorders, have been associated with aberrant changes in H3K9me3 levels. Different tools have been developed to enable detection and quantification of H3K9me3 levels in cells. Most techniques, however, lack live cell compatibility. To address this concern, we have engineered recombinant protein sensors for probing H3K9me3 in situ. A heterodimeric sensor containing a chromodomain and chromo shadow domain from HP1a was found to be optimal in recognizing H3K9me3 and exhibited similar spatial resolution to commercial antibodies. Our sensor offers similar quantitative accuracy in characterizing changes in H3K9me3 compared to antibodies but claims single cell resolution. The sensor was applied to evaluate changes in H3K9me3 responding to environmental chemical atrazine (ATZ). ATZ was found to result in significant reductions in H3K9me3 levels after 24 h of exposure. Its impact on the distribution of H3K9me3 among cell populations was also assessed and found to be distinctive. We foresee the application of our sensors in multiple toxicity and drug-screening applications.

Engineering Recombinant Protein Sensors for Quantifying Histone Acetylation

H3K14ac (acetylation of lysine 14 of histone H3) is one of the most important epigentic modifications. Aberrant changes in H3K14ac have been associated with various diseases, including cancers and neurological disorders. Tools that enable detection and quantification of H3K14ac levels in cell extracts and in situ are thus of critical importance to reveal its role in various biological processes. Current detection techniques of specific histone modifications, however, are constrained by tedious sample pretreatments, lack of quantitative accuracy, and reliance on high quality antibodies. To address this issue, we engineered recombinant sensors that are suitable for probing histone acetylation levels using various biological samples. The protein sensor contains recongition domain(s) with sequences derived from the bromodomain of human polybromo-1 (PB1), a natural H3K14ac reader domain. Various sensor designs were tested using nuclear extracts and live cells. The sensor containing dimeric repeats of bromodomain was found most effective in quantifying H3K14ac level in both in vitro and in situ assays. The sensor has a linear detection range of 0.5-50 nM when mixed with nuclear extracts. The sensor colocalizes with H3K14ac antibodies in situ when transfected into human embryonic kidney 293T (HEK293T) cells and is thus capable of providing spatial details of histone modification within the nucleus. Corrected nuclear fluorescence intensity was used to quantify the modification level in situ and found to correlate well with our in vitro assays. Our sensor offers a novel tool to characterize the histone modification level using nuclear extracts and probe histone modification change in live cells.

Actomyosin pulls to advance the nucleus in a migrating tissue cell

The cytoskeletal forces involved in translocating the nucleus in a migrating tissue cell remain unresolved. Previous studies have variously implicated actomyosin-generated pushing or pulling forces on the nucleus, as well as pulling by nucleus-bound microtubule motors. We found that the nucleus in an isolated migrating cell can move forward without any trailing-edge detachment. When a new lamellipodium was triggered with photoactivation of Rac1, the nucleus moved toward the new lamellipodium. This forward motion required both nuclear-cytoskeletal linkages and myosin activity. Apical or basal actomyosin bundles were found not to translate with the nucleus. Although microtubules dampen fluctuations in nuclear position, they are not required for forward translocation of the nucleus during cell migration. Trailing-edge detachment and pulling with a microneedle produced motion and deformation of the nucleus suggestive of a mechanical coupling between the nucleus and the trailing edge. Significantly, decoupling the nucleus from the cytoskeleton with KASH overexpression greatly decreased the frequency of trailing-edge detachment. Collectively, these results explain how the nucleus is moved in a crawling fibroblast and raise the possibility that forces could be transmitted from the front to the back of the cell through the nucleus.

Impact of antimicrobial ingredients and irradiation on the survival of Listeria monocytogenes and the quality of ready-to-eat turkey ham

Irradiation is an effective technology in eliminating Listeria monocytogenes, but it induces quality changes in meat products at or above specific radiation doses. To minimize irradiation-induced quality changes, only low irradiation doses are recommended. However, low-dose irradiation provides a chance for some pathogens to survive and proliferate during prolonged storage. To solve this problem, antimicrobial ingredients [2% sodium lactate (SL), 0.1% sodium diacetate (SDA), 0.1% potassium benzoate (PB)] and low-dose irradiation were combined and tested for their effects on the growth of L. monocytogenes and meat quality. The log10 reductions of L. monocytogenes in hams following exposure to 1.0 to 2.5 kGy of irradiation ranged from 2.0 to 5.0. The D10 values were 0.52 kGy for control ham or ham with PB, SL, or PB + SL; 0.49 kGy for ham with SL+SDA; and 0.48 kGy for ham with PB + SL + SDA (PSS). Addition of SL + SDA or PB + SL in combination with 1.0 kGy of irradiation was effective in suppressing the growth of L. monocytogenes for about 6 wk when stored at 4 degrees C, whereas 2.0 kGy of irradiation was listeriostatic. Ham irradiated with 1 kGy in combination with PSS was listeriostatic throughout storage. SL increased firmness of turkey hams, and sensory panelists noted that the saltiness was a little higher in products containing SL, but its overall impact on quality was minimal. Amounts of benzene were detected in irradiated hams with PB, showing PB was not fit as an antimicrobial ingredient for irradiated foods. In conclusion, 2% SL and 0.1% SDA in combination with low-dose irradiation were effective in ensuring the safety of ready-to-eat meat products against L. monocytogenes.

Influence of irradiation and storage on the quality of ready-to-eat turkey breast rolls

Influence of irradiation and storage on the quality of ready-to-eat (RTE) turkey breast rolls was investigated. Commercial oven roasted turkey breast rolls purchased from local stores were sliced and vacuum packaged. The sliced samples were randomly divided into 3 groups and irradiated at 0, 1.0, or 2.0 kGy using a linear accelerator. Color, 2-TBA-reactive substances (TBARS), sensory characteristics, and volatiles were evaluated at 0, 7, and 14 d of storage. Irradiation increased color a* value of turkey breast rolls. Irradiation and storage did not influence TBARS values. Sensory evaluation showed that irradiation significantly increased sulfury flavor. Because a dramatic increase in sulfur compounds was detected in irradiated samples, the sulfury flavor should be due to the sulfur compounds formed during irradiation. Irradiation also increased the amounts of acetylaldehyde, 2-methyl butanal, 3-methyl butanal, benzene, and toluene. It was concluded that irradiation significantly influenced the odor and flavor of RTE turkey breast rolls under vacuum packaging conditions. Therefore, strategies to prevent negative changes in the quality of irradiated RTE turkey breast rolls are needed.

The role of dietary vitamin E in experimental Listeria monocytogenes infections in turkeys

The current study was designed to determine if dietary vitamin E influenced either the gut clearance or levels of peripheral blood CD4+ and CD8+ T lymphocytes in adult turkeys experimentally infected with Listeria monocytogenes. Turkeys were fed vitamin E (0, 100, or 200 IU) from day of hatch to time of necropsy. After 6 wk on the experimental diet, turkeys were orally inoculated with L. monocytogenes (approximately 10(9) cfu). To monitor infection status, cloacal swabs were taken on selected days post-inoculation (DPI). At necropsy, samples of viscera, including liver, spleen, cecum, duodenum, ileum, and colon were collected and cultured for L. monocytogenes. In experiments 1 and 2, recovery of L. monocytogenes from cloacal swabs, tissues, and intestines from turkeys fed vitamin E was generally lower than that from turkeys fed the control diet, although these differences were not statistically significant. When data from both trials were combined, L. monocytogenes was cultured less frequently from cloacal swabs of the vitamin E-treated group (200 IU) on 2 and 3 DPI, when compared to controls (0 IU, P < 0.01). There were no changes in virulence characteristics of L. monocytogenes cells, as measured by in vitro killing of Ped-2E9 cells, recovered from cloacal swabs or tissues of experimentally infected turkeys fed the control or a vitamin E treatment diet. Flow cytometric analysis indicated that CD4+ and CD8+ peripheral blood T lymphocytes were elevated at 6 and 8 DPI in infected turkeys given 200 IU vitamin E.

Dietary fat, ketosis, and seizure resistance in rats on the ketogenic diet

PURPOSE

Fat is the major component of the ketogenic diet (KD), yet no studies have examined whether the type of fat used in the diet can be optimized to provide additional benefits. The purpose of the present experiments was to compare the efficiency of different fats in inducing ketosis and affording seizure resistance.

METHODS

The effects of KDs that incorporate lard, butter, medium-chain triglycerides (MCT), or flaxseed oil or a mixture of the latter three fats were examined in rats fed KD for up to 98 days. The maximal electroshock (MES) or pentylenetetrazole (PTZ) threshold tests were used to assess seizure susceptibility in two separate experiments.

RESULTS

The rank order of induced ketosis was MCT > mixture > or = flaxseed oil > or = lard = butter > or = control. MES failed to reveal anticonvulsant effects, but the PTZ test indicated that up to 50% of rats fed the KD were seizure protected (p < 0.05). The measures of seizure protection, seizure incidence and score, did not correlate, however, with the level of ketosis in the range of 0. 7-5.2 mmol/L for beta-hydroxybutyrate. In the long-term study, flaxseed oil KD maintained stable ketosis throughout 98 days, whereas ketones declined with lard and butter KD to the control level.

CONCLUSIONS

Seizure protection with the versions of the KD did not improve with the higher level of ketosis. The focus of the KD improvement, therefore, is not the achievement of higher ketosis per se but rather designing a diet that provides steady ketosis, exploits advantages of certain fats for neurological development or seizure protection via a nonketogenic mechanism, and is nutritionally balanced.

The MCT ketogenic diet: effects on animal seizure models

Male Wistar rat pups were weaned at 20 days of age and placed on either a control diet or a ketogenic diet containing medium-chain triglyceride (MCT) oil. After 10 days on the diets, they were subjected to one of four seizure tests-maximal electric shock, threshold electroconvulsive shock, threshold pentylenetetrazol, or maximal pentylenetetrazol. After testing, subjects were sacrificed and blood samples were analyzed for beta-hydroxybutyrate concentration. It was found that the MCT diet produced blood levels of beta-hydroxybutyrate that were comparable to or higher than those commonly reported in clinical studies. However, no anticonvulsant effects were seen in any of the seizure tests. In fact, the tests involving maximal seizures actually showed proconvulsant effects. It appears that clinical levels of ketones may be present in the bloodstream without suppressing seizures.

Steroid hormones affect limbic afterdischarge thresholds and kindling rates in adult female rats

Catamenial epileptics show particular vulnerability to seizures during menstruation and at the time of ovulation, when circulating estradiol (E(2))/progesterone (P(4)) ratios are high. The present study tested the hypothesis that alterations in neuronal excitability induced by E(2) and P(4) affect thresholds and the development of secondary generalization in kindled rats.

METHODS

The effects of endogenous hormones secreted during the estrous cycle, and of exogenous exposure to E(2) and P(4) after ovariectomy (OVX), with and without adrenalectomy (ADX), were tested. Kindling electrodes were implanted in the basolateral amygdala or dorsal hippocampus in adult female rats. The anticonvulsive effects of P(4) on amygdala kindled seizures were also determined in intact subjects.

RESULTS

In intact females, afterdischarge thresholds (ADTs) in the amygdala were significantly lower (306+/-48 microA; peak to peak) at mid-day proestrus, just prior to ovulation, when serum E(2) is elevated. ADTs were more than twofold higher (808+/-95 microA) during metestrus, coincident with peak ovarian P(4) secretion. In OVX females, amygdala thresholds were lowest with E(2) replacement and highest with P(4) replacement. Hippocampal ADT was unaffected by hormone replacement after OVX. The rates of both amygdala and hippocampal kindling were significantly accelerated by E(2) and slowed by P(4). E(2) replacement significantly increased serum corticosterone (CORT) levels. In ADX rats, CORT replacement increased kindling rates, synergizing with the effects of E(2). In fully kindled animals, P(4) administration suppressed motor seizures in approximately 60% of cases.

CONCLUSIONS

E(2) lowers amygdala ADTs and facilitates kindling. This effect may involve both direct E(2) effects and indirect effects mediated via increased levels of circulating corticosterone. P(4) raises amygdala ADTs, slows kindling development and suppresses fully kindled seizures. Hence, P(4) may have potential therapeutic value for women with catamenial epilepsy.

Inhibition of MAO-B by (-)-deprenyl alters dopamine metabolism in the macaque (Macaca facicularis) brain

The present study has examined whether MAO-B has a role in DA metabolism in the primate CNS in situ. Eleven macaques (macaca facicularis) were used in this study to examine the effects of (-)-deprenyl (1 mg/kg, i.v., 2 and 24 hours). (-)-Deprenyl administration completely and selectively blocked MAO-B activity and blocked DA metabolism in the caudate nucleus and frontal cortex. DA metabolism in the substantia nigra was not affected by MAO-B inhibition. Changes in DA metabolism were accompanied by changes in 5-hydroxytryptamine (5HT) turnover: 5-hydroxyindole acetic acid (5HIAA) levels increased in the caudate and decreased in the frontal cortex. Levels of 2-phenylethylamine (PE), a putative modulator of dopaminergic transmission, were increased by MAO-B inhibition in all three brain regions examined. It is concluded that in some regions of the primate brain, in contrast to the rat, MAO-B has an important role in DA metabolism.

Health status of children in foster care. The experience of the Center for the Vulnerable Child

OBJECTIVES

To describe the health status and to illustrate the usefulness of an enhanced primary care model for children in foster care.

DESIGN

Cross-sectional analysis of a clinical cohort via chart review.

SETTING

Foster Care Program of the Center for the Vulnerable Child at the Children's Hospital, Oakland, Calif.

SUBJECTS

Two hundred thirteen children in foster care assessed between August 1988 and June 1991.

INTERVENTIONS

None.

METHODS

A multidisciplinary assessment protocol was used to collect health and social histories and to conduct developmental, emotional, and behavioral assessments and medical examinations. Cross-tabulations were used to compare distributions of conditions and characteristics of the population, including the reasons for, timing of, and number of placements.

RESULTS

The population was largely African-American (83.4%), with a mean age of approximately 3 years. At least 78% of children came from homes where drug use was a primary reason for placement. A history of maternal drug use was present in 94% of infants. The number of placements ranged from one to eight (mean, 2.0). Placement changes were common. Over 20% of children had growth abnormalities, 30% had neurologic abnormalities, and 16% had asthma. Fewer than 20% of children had no medical conditions, while 28.8% had three or more conditions. Over 80% of children had developmental, emotional, or behavioral problems. Emotional, relational, and behavioral problems were more common in children first placed after 2 years of age and in those with a greater number of placements (chi 2 = 12.6, P < .05).

CONCLUSION

This comprehensive assessment of children in foster care revealed higher rates of chronic multiple medical and mental health problems than previously reported.

Maintenance on L-deprenyl prolongs life in aged male rats

The effect of l-deprenyl on longevity was examined in male Fischer rats. Subcutaneous injections of either l-deprenyl (0.25 mg/kg) or saline were given every other day starting at 23 to 25 months of age. The deprenyl-treated animals showed a significant increase in both mean and maximum survival. The differences were largest in the longest surviving animals, suggesting that an earlier onset for treatment may be beneficial. Analysis of body weights ruled out deprenyl-induced dietary restriction as an explanation for the group differences in survival. To the contrary, after about four months of treatment, the animals of l-deprenyl showed a slower rate of decrease in body weight than the controls.